1. Field
The following description relates to an optical pickup capable of implementing a tracking servo compatibly with optical information storage media having various types, and an optical information storage system including the same.
2. Description of Related Art
In order to implement a tracking servo, an optical pickup device may split light into zeroth-order light and first-order light by transmitting the light through a grating, and may perform an operation on signals which are obtained by detecting the zeroth-order light and the first-order light.
In the case of using a grating that has diffraction gratings on a single surface for a digital versatile disc-recordable (DVD-R) and a digital versatile disc-random access memory (DVD-RAM), a 2.5 track method is widely used. During the 2.5 track method, a zeroth-order light and a first-order light irradiated on an optical information storage medium are spaced apart from each other by about 2.5 tracks, and a tracking servo error is implemented using a detection signal that is obtained therefrom.
In the 2.5 track method, for example, when a two-wavelength light source is used, a pitch difference for a compact disc (CD) is relatively large. Thus, upon 2.5 track rotation on the DVD-R basis, a phase difference of about 45 degrees occurs in the case of CD-ROM 650 MB.
Therefore, when the 2.5 track method is implemented using a general grating with diffraction gratings on a single surface, it is difficult to precisely implement a tracking servo for a CD.